ML20214K312
| ML20214K312 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 05/19/1987 |
| From: | Leblond P COMMONWEALTH EDISON CO. |
| To: | Davis A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| 3068K, NUDOCS 8705280404 | |
| Download: ML20214K312 (2) | |
Text
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\\ Commonwealth Edloon
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One First Nabonal Plaza, Chicago, Illinois Address Reply 12 Post Omco Box 767
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May 19, 1987 y
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Mr. A..Bert Davis gn Regional Administrator U.S. Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, IL 60137
Subject:
Zion Nuclear Power Station Units 1 and 2 Main Control Room HVAC NRC Docket Nos. 50-295 and 50-304
Dear Mr. Davis:
Copies of four calculations involving the Zion control Room ventilation system were provided to W.D. Shafer on April 6, 1987, as part of the ongoing inspection regarding the September 11, 1986, radioactive release at Zion Station. These calculations were performed at the request of C.F.
Gill of your office.
Specifically, calculation No. ZI-6-87 was performed to estimate the postulated 30-day Main Control Room doses that might have been received had a LOCA occurred at Zion Station prior to the September 11, 1986 event. This calculation, when adjusted for the maximum integrated containment leak rate, yielded a maximum 30-day Control Room dose of 15.2 Rem. This is well below the 10 CFR 50, Appendix A, GDC 19 limit of 30 Rem. This dose projection is intended to be a conservative, but realistic estimate of the actual doses that control room personnel could have received.
This calculation also assumed the operation of a single Auxiliary Building Supply Fan. This condition is representative of approximately 50%
of Zion's operating history. The remainder typically involved operation with no supply fans running, resulting in no active air supply to the Auxiliary building. This results in roughly a factor of six reduction in Auxiliary Building flowrate.
An internal Commonwealth Edison Company technical review has identified that the dose model being utilized is highly sensitive to changes in auxiliary building flow rate. This model yields total doses that are inversely proportional to Auxiliary Building air.flowrate. Thus, the model would predict a six-fold increase in the total control room doses received in response to a six-fold reduction in air flow.
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8705280404 870519~
DR ADOCK 05000295 MAY 2 0193 PDR
4" A B. Davis May 19, 1987 This situation has been carefully reviewed by Commonwealth Edison personnel and their consultants. Commonwealth Edison Company believes that the dose model's sensitivity to auxiliary building flowrate does not represent an actual physical effect. Thus, it would not yield an accurate estimate of the actual doses that could have been received during the low-flow conditions.
In addition, the postulated effects of the airflow reduction on the calculation could be compensated for by the removal of additional, unnecessary conservatisms and through the use of more advanced computer modelling techniques. This information provides confidence that the previously supplied 30-day dose estimate of 15.2 rem remains a realistic, but yet conservative estimate of the actual doses that could have been received during a postulated LOCA.
Based upon the above information, Commonwealth Edison has no further plans to refine the control room dose calculations in support of the September 11, 1986, event. The estimate of 15.2 rem received over a 30-day time period provides a reasonable assessment of the safety significance of the ventilation discrepancies discovered on September 11, 1986.
This information was discussed with W.D. Shafer on April 14, 1987.
If any further questions arise regarding this matter, please direct them to this office.
Very truly yours, P A xe n J P.C. LeBlond Nuclear Licensing Administrator cc: Resident Inspector J.A. Norris - NRR 3068K
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